This invention relates to inkjet printers, and particularly to a technique for adjusting the printhead-to-paper spacing of an inkjet printer.
An inkjet printer includes one or more ink-filled cartridges that are mounted to a carriage in the printer body. The carriage is reciprocated across the width of the printer as paper or other print media is advanced through the printer. Each ink-filled cartridge includes a printhead that is driven to expel droplets of ink though nozzles in the printhead toward the paper in the printer. The timing and nominal trajectory of the droplets are controlled to generate the desired text or image output and its associated quality.
An important design consideration in connection with such printers involves the spacing between the printhead nozzles and the paper, which can be called the pen-to-paper or printhead-to-paper (PTP) spacing. Generally, the resultant print quality is highest when the PTP spacing is minimized. In this regard, minimizing the PTP spacing reduces print quality degradation from xe2x80x9cspray,xe2x80x9d which is the presence of small droplets having a trajectory that strays from that of the primary droplet. Moreover, minimizing PTP spacing is useful for minimizing the effects of errors that may be present in the trajectory of the primary droplet.
It is important, however, that this PTP spacing is sufficient to ensure that the printhead does not contact the paper, which could damage the printhead and/or smear the printed image. The possibility of contact may arise in instances where the amount and absorption of the liquid ink in the paper is such that the paper buckles upwardly, towards the nozzle. This buckling effect is known as xe2x80x9ccockle.xe2x80x9d Even in the absence of cockle, other factors, such as the tolerances between the parts that support the paper and printer cartridge, dictate the minimum allowable PTP spacing.
Versatile inkjet printers allow one to print onto print media having different thicknesses. A simple example of this is a printer that allows printing on conventional paper stock and a relatively thicker envelope. Best print quality is achieved, therefore, where the PTP spacing is adjusted to account for variations in paper thickness.
Color inkjet printers commonly employ either one colored-ink cartridge, which may be interchangeable with a black-ink cartridge, or two to four cartridges mounted in the printer carriage to produce black print or a full spectrum of colors. In a printer with four cartridges, each print cartridge contains a different color ink, with the commonly used base colors of black, cyan, magenta, and yellow.
Generally, the print quality of black-ink images or text is more sensitive to PTP spacing than is color image quality. Also, color-ink printing is likely to involve a number of passes over substantially the same area on the paper. Thus, the possibility of smearing the ink may be greater when colored ink is printed. Accordingly, it would be desirable to vary the PTP spacing during a print job that calls for both colored and black ink sections, thereby to optimize the PTP spacing for color and black printing.
Instantaneous PTP spacing control, whether undertaken during a particular print job or between sheets of paper having different thicknesses, can be characterized as dynamic control, as opposed to, for example, mechanical methods developed with impact printers or the like, which halt printing until some mechanical intervention (such as lever movement) takes place to adjust the PTP spacing.
The present invention is directed to an apparatus and method for dynamically controlling PTP spacing. To this end, the relative position of the carriage is selectively and dynamically changed to vary the PTP spacing. As one aspect of this invention, this control is provided by electronic actuation that requires no manual intervention by the printer user.
As another aspect of the invention, the control is provided via the printer control firmware, thereby employing the primary components of the printer control system that exist for controlling the printhead operation and carriage movement normally required for printing.
Other advantages and features of the present invention will become clear upon study of the following portion of this specification and the drawings.